Hatcher Pass Avalanche Forecast

Issued: Sat, Dec 09, 2017 at 8AM

Expires: Sun, Dec 10, 2017

Above 3,500ft Moderate

2,500 to 3,500ft Moderate

Below 2,500ft Low

Degrees of Avalanche Danger ?

1. Low
2. Moderate
3. Considerable
4. High
5. Extreme

Avalanche Danger Rose ?

Avalanche Problems ?

Problem Details

BOTTOM LINE

The peak of a natural avalanche cycle is behind us, after the Dec 2-3 storm that quickly overloaded the snowpack, spiking avalanche activity earlier in the week.

A SCARY MODERATE AVALANCHE HAZARD FOR TODAY, means that human triggering a dangerous avalanche is possible, but natural avalanches are unlikely. Stability on some slopes will be good, while others are not. If you see shooting cracks or hear whumphing, back off, these are bulls eye clues for a sensitive avalanche problem you don’t want to wrangle with.

Forecaster confidence in this advisory is low-moderate due to a week of poor visibility and tricky avalanche conditions. That said, we were able to get a good amount of testing done, a number of public observations were very helpful, but we were unable to safely assess and dig into the upper-most elevations.

Predicting and assessing this avalanche hazard may be difficult. The avalanche advisory is your starting point, from there you will need to peel the onion back, layer by layer. Back your team up, use conservative decision making, use safe travel protocol, travel one at a time, use safe zones and spotters, avoid slopes with terrain traps, employ radios for excellent communications and be practiced and prepared for companion rescue.

With sunny skies today, and beautiful powder, plus dangerous avalanche conditions elsewhere in the state, the human factor will be high for people getting out and recreating in Hatcher Pass’s backcountry. With one fatal accident already this season, have fun in the snow, but play it safe today. Focus on assessing the snowpack, dialing in your ever loosening travel protocol, enjoying safe riding terrain, and LIVE TO RIDE ANOTHER DAY.

Safer terrain is 25º and less and out of the runnout of steeper slopes from above.

5 hours and 31 minutes of daylight today. Sunrise at 10:03am, sunset at 3:35pm.


PERSISTENT SLAB AVALANCHE PROBLEM

Buried persistent weak layers continue to plague our snowpack. Expect these layers to be problematic throughout the season. While stability has improved since the most recent natural avalanche cycle earlier in the week, it is still possible to trigger avalanches.

Expect these persistent weak layers to continue to fluctuate through activation and inactivity throughout the season. Each time the snowpack is rapidly loaded with new snow, wind and/or rain, the balance will be tipped, and avalanches will occur until the snowpack slowly adjusts to the new load.

Buried persistent weak layers are widespread, but highly variable in sensitivity and thickness, on all aspects, at mid to upper elevation. Slope steepness plays a role, be extra cautious on slopes 35º and steeper, or in the runout of steep slopes from above. Slab avalanches can break above you, making escape difficult to impossible. It may be possible to trigger avalanches remotely or from below.

Expect leeward, wind loaded areas, generally Southwest to North, to have a thicker snowpack that may require more force to trigger, or if you find it’s thin, weak spot, to propagate a deeper avalanche, up 1-3′ deep, and up to D2 to 2.5. These areas may allow multiple riders to successfully recreate on a slope before the next one finally triggers it. Don’t be fooled by a false sense of stability. This tricky avalanche problem will be difficult to manage.

Thinner, weaker areas, may be more sensitive, producing shooting cracks, whumphing and more easily triggered avalanches.

No single instability test or pit will necessarily indicate a sensitive avalanche problem. You will likely find, through multiple tests, highly variable results. Certain areas may produce alarming test results, while others show moderate to good stability.

The good news is increased stability since the peak of the avalanche cycle earlier this week. The bad news is avalanches that are triggered may be larger in destructive size as the slab cohesion increases over time, but still rests on flawed layers of weak snow.

A heads up for ice climbers: Some of the ice climbs low in the canyon have large avalanche slopes above that feed into the waterfall ravines. While natural avalanches are not likely today, keep in mind that any new loading up high may affect these slopes in the future and increase the avalanche danger on these climbs.

LOOSE SNOW AVALANCHE PROBLEM

13″ of new snow from this week will be possible to human trigger on all aspects, at mid to upper elevation, on slopes 45° and steeper.  It will be tough to access this type of terrain and also avoid the persistent slab problem.

 

SNOWPIT PROFILE HERE


This snowpack is a lemon! …or a rotten pumpkin, whichever you prefer. Moderate to high strength, poor structure, variable to high propagation.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

One of a number of highly variable test results on a number of persistent weak layers in the snowpack.

 

Recent Avalanche Activity

No new natural or human triggered avalanches have been reported or observed since Dec 5/6.

See OBSERVATIONS for more information.

Recent Weather

This week’s weather at 3550′:

Temps averaged 28ºF, with a low of  19ºF and a high of  37ºF.

13 inches of new snow was recorded at IM snotel this week.

Overnight at 3550′:

Temperature averaged  29° F.

0″ new snow overnight.

This week’s weather at 4500′:

Temps averaged  24ºF, with a low of  18ºF and a high of  30ºF.

Winds averaged SE 13 mph, gusts averaging 35 , max gusts 60 mph.

Overnight at 4500′:

Temps averaged  28ºF overnight.

Winds averaged 4 mph overnight ESE to ENE, gusting 12 mph ENE at 7:00 am.


NWS recreational forecast for Hatcher Pass here


NWS point forecast here


State Parks snow report here

Additional Info & Media

The avalanche hazard will continue to slowly stabilize over time, until it is again overloaded due to rapid snowfall, winds, rain and/or thawing. Pay close attention to the weather. Watch closely for flagging on ridgetops indicating high winds and wind transported snow which could quickly increase the avalanche hazard.

The NWS rec forecast is calling for a high of 37°F at 3000′ today with warm overnight temps predicted to be 35ºF at 3000′. A lack of overnight freezing temperatures will weaken bonds in the snowpack and could increase the avalanche hazard.

 


A short video on the importance of always being ready for something you hope to never do… rescuing a partner from and avalanche burial.

 

Posted in HPAC Forecasts.

Observations

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